1. Field of the Invention
The present invention relates to a scanning device capable of reading information such as an image by using light and a fabrication method thereof, and particularly, to a scanning device having a micromirror constructed to improve structural stability and optical performance and a fabrication method thereof.
2. Description of the Background Art
Recently, a variety of Information transfer techniques using light as media for transferring all kinds of information have been developed. A technique for scanning information intended to be read by injecting a beam from a light source into a medium in which information is recorded is one of important techniques in the field of information transfer techniques using light.
The beam scanning technique is applied to various devices, for example, a barcode scanner, a projection display system having excellent color rendering capability with high resolution by using a laser scanning method, an HMD (Head Mounted Display) system and a laser printer.
In such a beam scanning technique, various scanning speeds and scanning ranges according to application examples to which the technique is applied are important factors for performance. In particular, in a system requiring for a high spatial resolution, a scanning mirror device capable of increasing angular displacement of a beam made incident and implementing a high scanning speed is required.
As one example of conventional scanning mirror devices, there is a polygon mirror device having a mirror in a polygon shape which is rotatably mounted to a motor being pivoted and is capable of implementing a high scanning speed up to several kilohertz (kHz). In the polygon mirror device, input light coming out of a light source passes through an optical system comprising a plurality of lenses, and is reflected by the polygon mirror in a direction where the polygon mirror is pivoted.
However, in case of a scanning device using the conventional polygon mirror, because of the limitations of rotation speed of a motor, angular velocity of the polygon mirror which depends on the rotation speed of the motor is also limited. Thus, it is difficult to increase the scanning speed. In addition, a structure that the scanning mirror is mounted on the motor increases the overall system in volume, makes it difficult to reduce power used for motor operation, generates problems with mechanical frictional noises from motor rotation, and increases the cost of production due to its complicated construction.
Accordingly, scanning devices having a micrometer structure whose entire system is small and which is manufactured using an MEMS technique capable of implementing a high scanning speed reaching tens of kilohertz (kHz) or using a general micromachining technique have been developed theses days. In the scanning device, a path of reflected light is changed according to rotation at a predetermined angle from side to side centering around torsion beams formed at both sides of the micrometer.
However, in case of the scanning device using the micrometer, since the micrometer is constructed to be extremely thin in comparison with its area, when the micrometer is operated with a high speed of tens of kilohertz (kHz), the micrometer flutters, that is, a dynamic deflection phenomenon occurs. Accordingly, a shape of a reflective surface of the micrometer is distorted and characteristics of reflected rays are deteriorated.